SUSCEPTIBILITY OF SELECTED COWPEA CULTIVARS TO CALLOSOBRUCHUS MACULATUS AND THE EFFECTIVENESS OF NEEM SEED OIL AS A STORAGE PROTECTANT IN YOLA, ADAMAWA STATE

SUSCEPTIBILITY OF SELECTED COWPEA CULTIVARS TO CALLOSOBRUCHUS MACULATUS AND THE EFFECTIVENESS OF NEEM SEED OIL AS A STORAGE PROTECTANT IN YOLA, ADAMAWA STATE

ABSTRACT

Cowpea (Vigna unguiculata L. Walp.) is a vital grain legume widely cultivated in tropical and subtropical regions, particularly in Africa, where it serves as a major source of dietary protein and household income. Despite its economic and nutritional significance, cowpea production and storage are severely threatened by insect pests, especially the cowpea bruchid (Callosobruchus maculatus), which causes considerable quantitative and qualitative losses during storage. This study investigated the susceptibility of selected cowpea cultivars to Callosobruchus maculatus infestation and evaluated the effectiveness of neem seed oil as a botanical protectant for stored cowpea grains in Yola, Adamawa State.

The experiment was conducted using a Completely Randomized Design (CRD) with three replications. Key parameters measured during the storage period included grain damage, insect mortality, weight loss, and the number of surviving insects. Results revealed significant differences between treated and untreated samples. Cowpea grains treated with neem seed oil recorded complete insect mortality, while untreated control samples exhibited continuous insect survival and increasing infestation levels over time.

The untreated samples showed substantial weight losses of 110 g, 240 g, and 350 g during the first, second, and third months of storage, respectively. In contrast, grains treated with neem seed oil recorded significantly lower weight losses of 10 g, 20 g, and 30 g during the same storage periods. Similarly, the percentage of seeds perforated by insects was considerably higher in untreated samples, reaching 36.87%, 69.54%, and 94.67% across the three storage months, whereas neem-treated grains maintained minimal damage levels of approximately 11% throughout the storage period.

The findings demonstrate that neem seed oil possesses strong insecticidal and protective properties against Callosobruchus maculatus, making it an effective and environmentally friendly alternative to synthetic insecticides for cowpea storage. The study therefore recommends the use of neem seed oil as a low-cost and accessible storage treatment for smallholder farmers to reduce postharvest losses and improve food security.

CHAPTER ONE

INTRODUCTION

1.1 Background of the Study

Cowpea (Vigna unguiculata L. Walp.) is one of the most important grain legumes cultivated in tropical and subtropical regions of the world. The crop is believed to have originated in Africa and belongs to the family Fabaceae. Cowpea plays a crucial role in food security and agricultural sustainability due to its high nutritional value and adaptability to harsh environmental conditions. It is consumed in various forms, including dry grains, fresh green pods, and leaves, while other parts of the plant are utilized for livestock feed and fiber production.

In many African countries, cowpea serves as a major source of affordable plant protein for rural and urban populations. The grain is rich in essential nutrients, particularly proteins, carbohydrates, and minerals, making it an important dietary component in regions where animal protein is scarce or expensive. Nutritional analyses indicate that cowpea grains contain significant protein content alongside other essential nutrients that contribute to human health and nutrition. Because of these characteristics, cowpea is sometimes referred to as “vegetable meat.”

Beyond its nutritional value, cowpea also contributes significantly to sustainable agricultural production systems. The crop has the ability to fix atmospheric nitrogen through symbiotic relationships with soil microorganisms in its root nodules. This biological nitrogen fixation improves soil fertility and reduces the need for synthetic fertilizers, thereby enhancing soil productivity and supporting environmentally sustainable farming practices. Cowpea is also highly tolerant to drought conditions and performs well in relatively poor soils, making it suitable for cultivation by smallholder farmers in semi-arid regions.

Globally, cowpea cultivation covers millions of hectares, with Africa accounting for the vast majority of production. Nigeria remains the largest producer of cowpea in the world, contributing a substantial proportion of the total global output. The crop is cultivated extensively across the savannah regions where climatic conditions are favorable for its growth. Cowpea production provides income opportunities for farmers, traders, and processors within the agricultural value chain.

Despite its importance, cowpea production and storage face numerous challenges, particularly from insect pests that significantly reduce yield and grain quality. One of the most destructive pests affecting stored cowpea grains is the cowpea bruchid, Callosobruchus maculatus. This insect pest attacks cowpea seeds both in the field and during storage, leading to rapid population growth and extensive damage to stored grains. Infestation by C. maculatus results in seed perforation, weight loss, reduced market value, and decreased germination potential.

The management of storage pests in cowpea has traditionally relied on the use of synthetic insecticides. While chemical pesticides can be effective in controlling insect infestations, their use is associated with several disadvantages. These include high costs, limited availability for smallholder farmers, environmental pollution, and potential health risks to humans and livestock. In many cases, improper application of chemical insecticides can also lead to pesticide residues in food products and the development of insect resistance.

As concerns about environmental safety and sustainable agriculture continue to grow, researchers and farmers are increasingly exploring alternative pest management strategies that are both effective and environmentally friendly. Botanical pesticides derived from plant materials have gained attention as promising alternatives to synthetic chemicals. Among these, neem (Azadirachta indica) has been widely recognized for its insecticidal, repellent, and growth-inhibiting properties against a variety of agricultural pests.

Neem seed oil contains biologically active compounds capable of disrupting the feeding, reproduction, and survival of insect pests. Because of its natural origin and relatively low toxicity to humans and non-target organisms, neem oil has been proposed as a sustainable option for protecting stored agricultural products. Evaluating the effectiveness of neem seed oil in controlling Callosobruchus maculatus infestation in stored cowpea grains is therefore essential for developing safer pest management strategies for farmers.

1.2 Statement of the Problem

Cowpea plays a critical role in ensuring food security and nutritional supply in many parts of Africa, particularly in Nigeria. However, the productivity and storage stability of cowpea grains are significantly threatened by insect pest infestations. Among these pests, the cowpea bruchid (Callosobruchus maculatus) is considered one of the most destructive storage insects affecting cowpea seeds.

Infestation by C. maculatus often begins while the crop is still in the field and continues during storage. The rapid reproductive cycle of the insect allows its population to increase quickly, resulting in severe damage to stored grains within a short period. In extreme cases, infestation can lead to almost complete destruction of stored cowpea grains, causing significant economic losses for farmers and traders.

To combat these losses, many farmers rely heavily on synthetic insecticides such as phosphine-based products and organophosphate chemicals. Although these chemicals can effectively control storage pests, their use presents several challenges. These include increasing costs, irregular supply in rural areas, risks of pesticide poisoning, environmental contamination, and potential hazards to consumers if residues remain in food products.

Furthermore, smallholder farmers in many rural communities often lack the technical knowledge required for the safe and effective use of chemical pesticides. This situation increases the risk of misuse and exposure to harmful chemicals. Consequently, there is a growing need to identify alternative pest control methods that are affordable, safe, and accessible to local farmers.

Plant-based insecticides such as neem seed oil have shown promising results in controlling storage pests while minimizing environmental and health risks. However, the effectiveness of such botanical treatments may vary depending on factors such as dosage, storage duration, and the susceptibility of different cowpea cultivars.

Therefore, there is a need to investigate the susceptibility of different cowpea cultivars to Callosobruchus maculatus infestation and to evaluate the effectiveness of neem seed oil as a potential botanical protectant for stored cowpea grains.

1.3 Justification of the Study

Postharvest insect damage remains one of the major constraints to achieving increased cowpea production and storage stability in many developing countries. In severe cases, insect infestation during storage can cause yield losses of up to 90–95%, particularly when effective pest management practices are not applied. Such losses not only reduce food availability but also affect farmers’ income and market supply.

Although several pest control strategies have been developed over the years, many smallholder farmers still rely on traditional storage practices that provide limited protection against insect pests. The use of synthetic insecticides, while effective, is often constrained by cost, accessibility, and safety concerns.

Botanical pesticides offer a promising alternative for managing storage pests in an environmentally sustainable manner. Neem seed oil, in particular, has attracted significant interest because of its strong insecticidal properties and wide availability in many tropical regions. It is relatively inexpensive and can be easily produced locally, making it accessible to small-scale farmers.

Investigating the protective effects of neem seed oil on stored cowpea grains could therefore provide valuable insights into sustainable pest management practices. Such research may contribute to the development of cost-effective and environmentally friendly storage methods that reduce postharvest losses and improve food security.

1.4 Research Questions

This study seeks to address the following research questions:

1.    What concentration and application rate of neem seed oil extract is most effective in controlling Callosobruchus maculatus infestation in stored cowpea grains?

2.    How does neem seed oil influence the survival rate and mortality of Callosobruchus maculatus during storage?

3.    What effects does neem seed oil treatment have on the quality and safety characteristics of cowpea seeds during storage?

1.5 Research Objectives

General Objective

The primary objective of this study is to investigate the susceptibility of selected cowpea cultivars to infestation by Callosobruchus maculatus and to evaluate the effectiveness of neem seed oil as a botanical insecticide for protecting stored cowpea grains in Yola, Adamawa State.

Specific Objectives

1.    To determine the optimal concentration and application rate of neem seed oil extract for controlling Callosobruchus maculatus infestation in cowpea seeds.

2.    To evaluate the survival response and mortality rate of Callosobruchus maculatus when exposed to neem seed oil and vegetable oil treatments.

3.    To assess the effects of neem seed oil treatment on the quality attributes and storage safety of cowpea seeds.